FI63886C - FOER FARING FRAMSTAELLNING AV ETT VARMVATTENBESTAENDIGT PLASTROER - Google Patents

Description

-iTfr— τ ΓβΙ Μ1ν advertisement publication qq ^ * 11) UTLÄGGNINGSSKRIFT 0 ^ 6 886 (45) Patent; .Jdelat T ^ (51) Kv.ik.3 / iw.a.3 B 29 D 23/04 SUOM I —Fl N LAN D (21) P »wnttll» lMimi · - PK «ntam» kninc 762637 (22) Htk «ml« pUvt - AMBknlngtdag 15. 09.76 (23) AlkupIJvl — Glltightttdac 15.09.76 (41) Tullut JulklMkal - Bllvlt off «ncHg _. n PMtti and register board (44) NU, ay «k..pu« n k-LMk ^ m '*

Patents and registries' Antökan uttegd och wi. * Krift * n puMtcand 31.05. Ö3 (32) (33) (31) Requested «toiksut — fegird prtorit« t (71) Allgemeine Synthetische Gesellschaft Etablissement, Hauptstrasse 33, 9 ^ 90 Vaduz, Liechtenstein (Li) (72) Andre Jacques Schaerer, Pfaffhausen, Switzerland-Schveiz (CH) (7 * 0 Leitzinger Oy (5 * 0 Method for the manufacture of hot water-resistant plastic pipes - Förfarande för framställning av ett varmvattenbeständigt plaströr

The invention relates to a method for manufacturing a hot water-resistant plastic pipe, in particular for building installation purposes, which plastic pipe is formed by an inner pipe extruded from a network-bonded polyethylene or a crosslinkable polyethylene copolymer and which after extrusion is

Swiss patent publication 434 716 has already proposed plastic pipes in which the inner pipe in direct contact with the hot water is a crosslinked olefin polymer or an olefin copolymer, for example polyethylene, and in which the inner pipe is surrounded by an outer jacket. Such plastic pipes offer a number of advantages over ordinary installation pipes made of galvanized steel or copper for hot and cold production water and hot water central heating. In this context, particular emphasis should be placed on their corrosion resistance, low cost, thermal insulation, odorlessness, tastelessness, longevity, physiological safety and easy portability, and finally simple connectivity to fittings, fittings and the like that do not require threaded, soldered or welded joints. However, it is very important that

t · · I

plastic pipes equipped with optimally network-bound 2 <3? P f '· polyethylene inner pipe, in contrast to non-crosslinked polyethylene plastic pipes, is also not sensitive to stress corrosion or stress cracking that may otherwise occur in pressurized hot water pipes.

Despite the mentioned advantages of plastic pipes with a crosslinked polyethylene inner pipe, so far it has not been possible to>. to provide a suitable and further cost-effective method of manufacturing such pipes. If an attempt is made to make a pipe from crosslinked polyethylene in the manufacture of plastic pipes according to conventional extrusion methods, then it can be stated that the known working methods are not applicable. If an attempt is made to crosslink the peroxide-containing polyethylene as it flows through the extrusion tool, the crosslinking is obtained only on the outside of the tube, which moves along the inner wall of the tool heated to the crosslinking temperature. However, the occurring crosslinking causes an increase in the viscosity of this boundary layer, as a result of which different material flows are created in the cross section of the pipe wall, which makes continuous extrusion impossible. Also, the proposal to first make a tube from a non-crosslinked thermoplastic polymer according to the extrusion method, i.e. to extrude the tube below the crosslinking temperature and then convert it to a crosslinked state (Swiss Patent Publication 434,716), has proved unfeasible. This method proposal contradicts the feature of the peroxide-containing tube that, before the crosslinking temperature is reached, virtually no rigidity is present in the melting region and the product collapses on its own. However, an attempt to circumvent this disadvantage by always adding 60% by weight of carbon black to the polyethylene before extrusion, so that the pipe also retains the shape of the polyethylene in the melting range and can crosslink without damaging the shape, results in a very rigid pipe with this high soot content. count only as straight pieces.

The object of the present invention is to provide a method of the quality described in the introduction which overcomes the difficulties presented and which, in a simple manner, makes it possible to produce a flexible plastic pipe resistant to both hot water and pressure.

This is achieved according to the present invention by 3 6 3 8 8 (- only the moon's extruded inner tube is provided with an outer jacket, the combined tube thus obtained is subjected to a heat treatment which causes crosslinking and in which the gas overpressure is maintained by the inner tube crosslinking reaction. at least in the first stage.

The outer jacket fitted on the inner tube before the mesh bonding allows the overpressure to be maintained in the inner tube during the heat treatment, which causes the mesh bonding of the inner tube without stretching outward under the effect of the overpressure. On the other hand, the internal pressure in the inner tube prevents the inner tube from collapsing in the critical temperature range during the first stage of the heat treatment. In this way, as simple as it is efficient, the polyethylene inner tube maintains its circular cross-section at the mesh bond temperature. The plastic tube according to the invention has a mirror-clear inner surface of the inner tube, which prevents the formation of scale and limescale build-up and further reduces the flow resistance of the tube. so as to provide a two-layer assembled pipe. In later use, the outer jacket gives the combined pipe the necessary strength so that the pipe produced according to the method not only becomes heat-resistant, but at the same time can also receive an increased internal pressure. Depending on the quality of the outer jacket used, the cracking pressure of the plastic pipe can be achieved at a working temperature of 70 ° C up to 2 2 about 40 kp / cm, which at a working pressure of 4 kp / cm means a tenfold safety factor.

The process can use a high-pressure polyethylene granulate having a melt index range of 0.8 to 5 and containing in a uniformly distributed form a peroxide having a minimum decomposition temperature higher than 135 ° C, keeping the temperature of the polyethylene pulp during melting and extrusion below the decomposition temperature of the peroxide used. Also, when the temperature of the polyethylene pulp in the extruder is kept only reasonable and uniform below the minimum decomposition temperature of the peroxide, the net bonding of the polyethylene in the spiral f 6 3 8 8 f 4 cylinder or pipe tool is also certainly prevented. Peroxide, which hajoamisläm lowest-temperature is higher than 135 ° C, working also takes care of the fact that the network binding is eliminated during extrusion. The above-mentioned preferred process conditions allow the continuous production of a peroxide-type inner tube from non-crosslinked polyethylene.

The method according to the invention is preferably carried out in such a way that the heat treatment is carried out at a temperature between 135 and 200 ° C, preferably between 135 and 180 ° C in a time range of 0.5 to 7 h. The higher the network bonding temperature, the shorter the network recovery. It has been found that complete crosslinking, which is always pursued in the process according to the invention, can also be achieved in a relatively low temperature range of 135 to 140 ° C, while at the same time extending the heat treatment time to about 7 hours. In this case, it is possible to make the outer jacket by extruding a layer of polypropylene applied to the inner tube without this polymer losing its shape at a given crosslinking temperature or cracking under the effect of the overpressure transmitted in the inner tube.

The heat treatment of the composite tube is suitably carried out by winding the composite tube after the outer jacket has been applied and subjecting it to a heat treatment which causes 'net bonding', in this form in the furnace. Since the flexibility of the composite pipe allows it to be wound without intolerable cross-sectional deformation, the machining can be performed as described very simply.

According to the inventive idea, during the heat treatment 2 an overpressure of 0.2 to 2 kp / cm of air is maintained. It has been found that this overpressure is quite sufficient to certainly prevent the polyethylene inner tube from collapsing as it passes through the melting temperature to initiate crosslinking and the associated increase in viscosity. The deformability of the inner tube does not require that the internal pressure be maintained throughout the heat treatment process, but in many cases it is sufficient to maintain the internal pressure long enough for the degree of crosslinking to be sufficient to prevent the tube from collapsing. Of course, there are no obstacles to maintaining the internal pressure throughout the heat treatment.

· '' M: '5 6 3 8 8 6

In order to provide a very flexible composite pipe, it is suitable that the outer jacket be placed on top of the inner pipe by extrusion and that it be a temperature-resistant thermoplastic. Particularly suitable for this are polypropylene, polyamide, polycarbonate, ethylene-propylene copolymer, ethylene-butadiene-styrene tripolymer or elastomeric polyester-isocyanate polymer. The strength of the outer jacket wall is determined for the required creep strength, taking into account that the pressure that must be withstood when used in the household of 2 plastic pipes is at least 4 kp / cm at 70 ° C. In this case, it must be taken into account that when a plastic pipe made according to the invention is used in building installations, it is intended to be installed in concrete and that it is then surrounded by hardened concrete in the installed space. This receives at least a certain amount of pressure load on the pipe, which advantageously affects the creep strength as an additional safety factor.

However, for enclosing the inner tube with a sheath using a thermoplastic, the method can also advantageously be implemented in that the outer sheath is made by twisting or braiding paper or fibers, such as glass fibers, viscose fibers, man-made fibers or cellulose fibers, onto the inner tube. By reinforcing with these substances, the creep strength of the plastic pipe made according to the invention can be further increased. In order to protect the outer sheath applied in this way, it is suitable to apply a thin-walled, synthetic resin coating on the wrapped or braided outer sheath. In this case, the coating is suitably polypropylene or polyamide resin and is applied by extrusion.

However, the method can also be carried out according to a modified embodiment by introducing a thermosetting resin into the outer sheath during twisting or braiding, which resin is then cured simultaneously with the heat treatment which causes the crosslinking. In this case, the resin penetrates the fibers or strips and binds them into a very pressure-resistant outer sheath. In this way, for example, the paper strips can be impregnated with phenolic resin and wrapped around an inner tube of polyethylene.

To increase the flexibility of the outer sheath, the strips can be placed corrugated around the inner tube. If the pipe has to be made for high working pressures, the inner pipe is suitably surrounded by flat or corrugated strips provided with a reinforcing metal film.

6 6 3 8 8 6

For very high operating pressures, it is preferred that a leaded steel strip be wound on the corrugated pipe. The composite pipe made in this way has high pressure resistance.

It is not necessary to extrude, wrap or braid the outer casing over the inner tube. On the other hand, it is also possible to use a metal tube as the outer sheath, which tightly surrounds the inner tube, into the metal tube of which the inner tube is pulled. More suitably, aluminum, aluminum alloy or steel pipes with a length of about 6 to 20 m depending on the cross-section and the strength of the wall are used. If the wall is sufficiently thin-walled, the composite pipe thus produced can also be easily and continuously continuously bent, possibly coiled before the heat treatment required to achieve the mesh bonding. In addition to building installation purposes, such plastic-reinforced plastic pipes are advantageously useful for many applications in the chemical industry, where they are particularly suitable for conducting corrosive substances and have great advantages over ordinary rubber-clad pipes.

By using a metal tube as an outer jacket, it is easier to retract the inner tube if its diameter is reduced during retraction with a sufficient axial tensile load. It has been found that there is excellent adhesion between the inner tube and the metal tube after the crosslinking reaction. For this purpose, it is suitable to degrease the metal tube before retracting the inner tube.

If heat-resistant polypropylene is used as the jacket of the polyethylene inner tube and dicumyl peroxide is used as the crosslinking agent, then a curing time of 6 h is required in the heat treatment furnace at the crosslinking temperature of 135 ° C to achieve complete crosslinking.

If a paper strip impregnated with a thermosetting resin, for example phenol-melamine epoxy polyester resin, is used to make the outer jacket on the inner tube, the temperature of 160 ° C required to cure the thermosetting resin can be used to crosslink the polyethylene inner tube.

In order to improve the thermal insulation of the plastic pipe made according to the invention, an insulating jacket made of foam can be placed on the outer jacket 6 3 8 8 ^ 7 by extrusion. This insulating sheath does not bond to the outer sheath of the plastic pipe beneath it, so the tube formed by the inner tube and the outer sheath can freely expand inside the insulating sheath when the plastic pipe is installed inside the concrete. For this purpose, a glass fiber coil or braid is suitably selected as the outer sheath, which is then surrounded by an extruded foamed polyethylene having closed cells by an extrusion process. Even after the insulation jacket has been made, the plastic pipe made according to the invention is flexible enough to allow easy installation.

Even without an additional insulating sheath, the plastic pipe according to the invention has excellent insulating properties, while the thermal conductivity of the inner pipe made of crosslinked polyethylene rises only to 0.22 kcal / h x m x ° C at 80 ° C. The plastic pipe made according to the invention is so flexible that it can be placed and fastened by simple unrolling of the roller from the connection point to the downspouts between the steel beams before being fitted to the concrete. This makes it possible to lay the hot water line from the riser in layers on the concrete floor, which means a considerable saving in installation costs. The plastic pipe made according to the invention can also be placed in grooved brick walls and fixed with mortar at no greater cost. Of course, the plastic pipe made according to the invention can also be used for cold water.

It is also suitable for conducting other substances at elevated temperature and pressure.

The mechanism of the crosslinking reaction of polyethylene is known and does not require a detailed explanation here. The crosslinking of polyethylene takes place immediately by linking the polymer groups formed by the action of suitable organic peroxides, preferably to tertiary carbon atoms, i.e. to the branching centers of the polyethylene. The formation of polymer groups is the basis for the dehydration effect, in which the hydrogen of the tertiary carbon atom of polyethylene is transferred to the oxy group of peroxide in heat. The peroxide cleavage product forms volatile compounds that are virtually completely removed from the crosslinked polyethylene by heat. The crosslinking of polyethylene promotes decreases in its fluidity at elevated temperatures and reduces its solubility in organic solvents. The increasing degree of crosslinking manifests itself both in an increase in mechanical strength at elevated temperatures and in a decrease in solubility in certain solvents, correspondingly in a decrease in fluidity. Changes in the properties of both 8 6 3 8 8 6 make it possible to determine the degree of network commitment obtained. With the best possible crosslinking, the formation of stress cracks is also completely eliminated, with the result that the crosslinked polyethylene becomes very suitable for the production of hot water pipes.

Due to the fact that the crosslinking temperature and, the crosslinking time in the heat treatment can be chosen as desired, both parameters are adjusted so that the desired complete crosslinking of the inner tube takes place. The simplest way to measure the degree of crosslinking is to determine the gel content, i.e. to determine the insoluble proportion of crosslinked polyethylene. In this case, 0.3 g of the crosslinked polyethylene sample is extruded as fine particles in a Soxleth extruder in pure toluene, xylene or decalin for 6 hours. The sample is then dried under vacuum to constant weight and weighed. The weight difference corresponds to a gel extracted from non-crosslinked polyethylene and is inversely proportional to the degree of recovery of your net.

In addition to these accurate measurement methods, a relatively simple test method can also be used, which allows continuous quality monitoring. In this case, the degree of crosslinking is continuously tested by immersing small parts of the carbon black-containing polyethylene tube in boiling toluene. Only when taking a sample that does not stain boiling toluene should this be considered as an indication that the inner tube no longer contains any non-crosslinked polyethylene.

A number of peroxides are suitable for the crosslinking reaction. Thus, for example, the following peroxides can be used: 2,5-dimethyl-2,5-di (t-butylperoxy) -hexane, dicumyl peroxide with a peroxide content of 40% and 60% of the support and a half-life at 180 ° C of 60 s, and di -tert.butyl peroxide with a peroxide content of 97% and a half-life at 180 ° C of 180 s.

The method according to the invention is illustrated in more detail by means of the following few examples.

9 63886

Example 1

Store the usual suurpainepolyeteenigranulaattia (Lupolen 1852 E, manufactured by BASF.) having a melt index of 0.4 - 0.6, a density of 0.93, the amount of finely divided carbon black of 2.5 weight percent and the average grain size of 3 mm, was passed in an amount of 30 kg Rheinstahl AG to a Henschel-type instant mixer and 600 g of 2,5-dimethyl-2,5-di (t-butyl peroxide) -hexane were added and mixed efficiently. The resulting temperature rise was stopped at 60 ° C by stopping stirring. In the mixture thus obtained, the peroxide had diffused mainly into the granulate. After intermediate storage and cooling, the polyethylene granulate prepared in this way was placed in a heated B 45 type extruder with a length to diameter ratio of 20: 1 manufactured by Kuhne GmbH, Kunststoffmaschinenbau, with a short compression zone and melted at 130 ° C and extruded 12 mm, outer diameter 16 mm and throughput speed 3 m / min. and wound on a drum after cooling.

A flexible, form-retaining and heat-resistant corrugated tube (grooved tube) of leaded steel strip with a thickness of 0.12 mm and a width of 20 mm, manufactured by Kopex Rillenrohrautomaten from Plica AG, Riischlikon, Switzerland, was wrapped over the obtained inner tube.

The resulting flexible combined tube was kept in a drum-wrapped space for 2 hours in an oven at 180 ° C. In this case, an overpressure of 1.8 kp / cm was maintained in the connected tube.

The degree of crosslinking of the mirror-clear inner surface of the cooled composite tube was 100%. The degree of crosslinking was tested by exposing a portion of the tube to an inner tube which was cut into small pieces placed in boiling toluene. Even after boiling for 15 minutes, toluene remained water clear from the solution in the absence of crosslinked polyethylene bodies. In the burst pressure test, the combined pipe was continuously exposed to an elevated maximum pressure of 25 kp / cm with water at a temperature of 70 ° C. This internal pressure corresponded approximately 5-6 times the internal pressure of the financial lines. The combined pipe withstood this internal pressure, which, in the absence of the higher pressure conditions of the equipment used, could no longer be raised by the changes. Several tube samples were subjected to a stress cracking formation test according to ASTM D 1693-60 T. In no case did the formation of stress cracking occur

Example 2

Store the usual eteenivinyyliasetaattikopolymeraattia (Lupolen A 3510 D, manufactured by BASF) was stirred vigorously in granules, having a melt index of 3.4 - 4.6, a density of 0.934 and a carbon content of 2 percent by weight, 20 kg in combination with the example 1 corresponding to 300 g of 1 , 3-bis (tert-butyl peroxide-isopropyl) benzene. The prepared copolymer was fed to the extruder used in Example 1 and melted at 135 ° C and extruded into a tube / having an inner diameter of 12 mm and an outer diameter of 16 mm at a flow rate of 10 m / min. and wrapped in a drum after cooling.

A 20 mm wide glass strip weighing 150 g / xn was wrapped on the obtained inner tube under a draw of 2 pcs. The resulting combined tube was then subjected to heat treatment for 4 hours wrapped in a drum in an oven at 160 ° C. In this case, an overpressure of 1 kp / cm of air was maintained in the connected pipe. After cooling, a composite tube with a degree of crosslinking of 100% was coated with a 1 mm thick foam polyethylene sheath. The combined tube thus obtained had a very good flexibility. After the composite pipe is laid in the cement, it can easily expand inside the foam jacket. Attempts to break the pipe thus fabricated and laid in concrete failed at high cracking pressures.

Example 3

A polyethylene inner tube having an inner diameter of 12 mm and an outer diameter of 15.9 mm made according to Example 1 was pulled with a traction force of 30 kp into a 10 m long thin-walled aluminum tube having an inner diameter of 16 mm and an outer diameter of 18 mm. By drawing the inner tube by drawing slag, its diameter was reduced in a small amount, which facilitated the retraction of the aluminum tube. After retraction, the tensile load was stopped, followed by the return of the inner tube to its original diameter and the removal of air between it and the aluminum tube. The internally coated aluminum tube was then wound and kept in an oven at 160 ° C for 4 hours under an internal pressure of 1.5 kp / cin.

The combined tube thus obtained had very good chemical resistance, low weight and high compressive strength (more than 50 kp / cm 2 at 70 ° C).

11 6 3 8 8 6

It could be bent ehlposti by hand. The groups obtained by the crosslinking reaction provided a very good bond between the 100% crosslinked polyethylene and the inner wall of the aluminum tube. At a temperature of 120 ° C and a vacuum of 10 mm Hg in the inner tube, no separation of the polyethylene tube from the aluminum tube wall was observed. Using the inner tube prepared according to Example 2, similar results were obtained.

Additional experiments with a composite pipe with steel pipes of different wall thicknesses as the outer sheath gave consistency with the properties of an internally coated aluminum pipe with an inner pipe made of polyethylene. The increasing wall thickness of the steel pipe only made it difficult to bend the composite pipe.

In addition to polyethylene and said copolymer, other copolymers such as ethylene propylene and ethylene ethyl acrylate can also be used to make the inner tube to provide an even more flexible plastic tube. By using a copolymer having a melt index of 3, the throughput rate in the extruder can be increased to 10 m / min, since the feed rate of the material can be increased by increasing the screw speed without the material temperature rising above 130 ° C due to frictional heat.

The use of a low carbon black content in the inner tube extrusion pulp is considered advantageous for carrying out the method according to the invention, since the added carbon black is an excellent indicator for controlling the degree of crosslinking, as previously described. In addition, the soot protects the polyethylene against harmful UV radiation and acts as a heat stabilizer. Commercially available common grades of polyethylene used to make high quality water line pressure pipes usually have a soot content of about 2% by weight.

• S '· r.

Claims (4)

6 3 8 8 6 12 A method of manufacturing a hot water-resistant plastic pipe, in particular for building installation purposes, comprising a plastic pipe extruded from a crosslinkable polyethylene or a crosslinkable polyethylene copolymer and which, after extrusion, is provided with an outer jacket, the composite pipe thus obtained is subjected to a heat treatment which causes crosslinking and in which the gas overpressure is maintained in at least the first stage of the crosslinking reaction of the inner tube. Process according to Claim 1, characterized in that the heat treatment is carried out at a temperature between 135 and 200 ° C, preferably between 135 and 180 ° C in a time range of 0.5 to 7 hours. Method according to one or more of the preceding claims, characterized in that the combined tube is rolled after being placed on the outer sheath and subjected to a heat treatment which causes net bonding, in this form in an oven. Method according to one or more of the preceding claims, characterized in that an air overpressure of 0.2 to 2 kp / cm is maintained during the heat treatment.